[uoaei]

50% of my miles and 90% of my travel time is on a bike.

Signalling a change in direction should only be done with your left hand, per manuals.

Braking can be achieved with only the right hand (rear brake, typically).

Dismounting and signalling/braking is hard to do at once though. And you're right it should be obvious that a cyclist is turning left if they are in the left turn lane.